In the manufacture of substrates for various applications such as magnetic disks for disk drives, it is often important to implant particular materials on the substrates. Currently, nitrogen implantation is performed on two disks simultaneously using a sputter tool designed to give high throughput. To facilitate the implantation, RF power is applied to a carrier holding two disks/substrates under the influence of a magnetic field. The presence of the magnetic field increases the plasma density and the rate of nitrogen implantation. The magnetic field is produced by four ring magnet packs which are held stationary in front of each of the disk surfaces of the two disks. However, due to the magnetic field interaction between the different magnet packs, nitrogen implantation is not uniform between front and rear disk surfaces. In addition, the nitrogen implantation is not uniform from the first disk as compared to the second disk. As such, there is a need for a system and method for uniformly implanting a preselected material on substrates using magnetic fields.